Building Manager

TRVs

Hi-  I'm assuming that what you are calling "Thermostatic Actuators" are what is also more commonly know as TRVS (Thermostatic Radiator Valves) and to answer your question these can be placed just on individual radiators to control over heating in that room. There is no need to place them on every radiator in the building.



There are several types of TRV and while most generally work on the same basic principle it is very important to obtain the model that works on your type of steam system. Since you stated you have a one pipe steam system you must get the TRVs that are made specifically for a one pipe steam system.  A TRV for a one pipe steam system is attached to the radiator where the radiator vent (valve)  is normally located and is installed between the radiator and the radiator vent (valve).  The TRV for the one pipe steam system also includes a Vacuum Breaker that is either external or build into the TRV. (More on the reason for vacuum breaker below)



Operation: The temperature setting on the TRV can be set any where from 42 degres F to around 90 degrees F by adjusting the temperature knob.  When the thermostat calls for heat, the boiler turns on and generates steam. The steam travels into the radiator and pushes the air out the vent hole, through the TRV which is open (because the room temperature is below the temp setting on the TRV) and out through the radaitor vent (valve). When steam reaches the vent hole, it travels through the open TRV  but on reaching the vent ,the vent closes just as it would without the TRV.  This cycle will continue until the room temperature reaches the temp setting on the TRV at which time the TRV closes which stops any air being released through the radiator vent (valve). However while there is  steam pressure, there is still steam being condensed in the radiator.  This is where the vacuum breaker comes into play. When the boiler cycles, a vacuum is formed in the radiator and the vacuum breaker allows air to enter the radiator. When the boiler starts supplying steam again the TRV being closed doesn't not allow the air to escape through the radiator vent (valve) .Since there is air in the radiator, steam can't get in and heat the radiator and the radiator cools.  When the room cools below the Temp setting on the TRV, the TRV opens and the whole TRV cycle starts again.



You mentioned that Dan's article suggested that you use the same model valve (vent) through out the building. This is true when it relates to just radiator vents (and even then there are some exceptions)

The following is some information and notes on two popular TRVs:

On the Danfoss model the vacuum breaker in internal and on the Macon it is external.



Macon 1 pipe TRV  Here is a link with info on the Macon - http://www.maconcontrol.com/opsk1204.html

Note that the Macon comes with a radiator vent (valve). On the Danfoss the installer must provide the radiator vent (valve).  When comparing pricing keep this in mind.

Danfoss 1 Pipe TRV - See attached pdfs

The Danfoss is also  available with a remote thermostat .

It can be had with an anti tamper device so you can lock the settings if desired.

Radiator vents - The radiator vent (valve) on the TRVs must be straight vents rather than the 90 degree angles vents you normally use on radiators. You can still use the angle vents but will have to place to 45 degree elbows together to orient the vent in the vertical plane.

On of the concerns with using these in an apartment is whether the boiler cycles off causing vacuum to be formed in the radiators so the air can reenter through the vacuum breaker. You also don't want to use a TRV in the same room that has the thermostat that controls the boiler.

I hope this has helped answer your questions. What I would do is get one TRV and just try it out so you can judge how well it operates in your system. Try either State Supply or Pex Supply on the internet as I believe they carry these TRVs

- Rod